1. Field of Invention
The present invention pertains to the field of systems. More particularly, this invention relates to system application techniques using time synchronization technology.
2. Art Background
Distributed control systems are commonly arranged as a collection of nodes which are interconnected via one or more network communication links. These network communication links may be packetized links such as Ethernet or one or more of a variety of other packetized links that are adapted to distributed control system applications.
Distributed control systems commonly benefit from precise control of the timing at the distributed nodes. U.S. Pat. No. 5,566,180 of Eidson et. al. provides a method and apparatus for providing precise control of timing in distributed nodes by synchronizing the local clocks in the distributed nodes. In many applications, it may be desirable that the time kept by the distributed nodes be traceable to a standard time. Such may be useful in applications, for example, in which events in the distributed nodes must accurately occur with respect to a particular date and/or time of day.
A method and apparatus is disclosed for accurately distributing traceable time values to a set of nodes in a system. Each node includes a slave clock that synchronizes a slave time value using a synchronization protocol. The system includes a traceable time source that generates a traceable time value and a master node having a master clock that synchronizes a master time value to the traceable time value and that distributes the master time value to the slave clocks via the communication link. The nodes may be distributed nodes or cards connected to a backplane. Also disclosed are a variety of techniques for distributing the information associated with the synchronization protocol and a variety of applications for the synchronized timing in the slave nodes.
Other features and advantages of the present invention will be apparent from the detailed description that follows.